1. Field of the Invention
The present invention pertains to a the power supply for medically implanted device, and more particularly, pertains to a battery-discharge method for powering an implanted defibrillator device.
2. Description of the Prior Art
In defibrillators available today, both implantable and external, energy is delivered to the electrodes by the discharge of capacitors. Prior to the shock initiation, a converter circuit is typically used to charge a high-energy capacitor to a high voltage ranging from several hundred volts in an implantable device to several thousand volts in an external device. Because capacitors are relatively space-inefficient, as energy-storage devices characteristically are, 2 joules/cc for an aluminum electrolytic capacitor, the output capacitors are the largest components in a defibrillator. This is not a major problem in external defibrillators, but it is a critical problem in implantable defibrillator systems. Many attempts to develop higher energy density capacitors have been made in the last five years with the objective of possibly doubling the energy density of aluminum electrolytic capacitors without success. The present invention discloses a method of storing and delivering the same energy to the heart from a device with 2 to 3 orders of magnitude more energy density than conventional capacitors.
Prior art devices have failed to provide a means that is compact for storage of an electrical charge for an implanted defibrillator device. Prior art systems employed capacitors that were large and bulky and that took up an inordinate amount of space in the implanted device.
The present invention overcomes the disadvantages of the prior art devices by providing a electrochemical charge-storage system having a plurality of switched cells to provide an electrical charge for an implanted defibrillator system.
The present invention adapts, for implantable medical-electronic systems, a concept employed in other contexts and technologies. A prior art technique for achieving high voltages that predates even solid-state electronics employs an array of capacitors. By charging them in parallel from a relatively low-voltage supply, and then connecting the capacitors in series by means of a switching network, one creates the condition for a high-voltage capacitor discharge. The present invention makes a major improvement on this technique.